X-ray detectors, such as flat panel X-ray detectors (FPXDs), have been introduced and widely used in medical industries and the like.
An X-ray detector includes a scintillator and a sensor panel. The scintillator is configured to convert incident X-ray into light. The sensor panel is provided, with a plurality of pixels and a switching element. Each pixel includes a photodiode that receives light from the scintillator and converts the light into an electric signal. The switching element is connected to an output terminal of the photodiode to output the electric signal. The sensor panel may further include a signal detector and a gate driver. The signal detector detects the electric signal output from the pixel. The gate driver turns on the switching element to enable the signal detector to detect the electric signal. The electric signal detected by the signal detector is converted into an image signal through a predetermined process performed by a controller or the like provided in a main board. The image signal is transmitted to a display device for displaying an X-ray image.
Between an X-ray incidence and the next X-ray incidence, the X-ray detector performs a reset process to equalize electric charges stored in the photodiodes of the plurality of pixels. This process is required for removing a residual image caused by previous X-ray incidence.
Generally, as the reset process occurs, the photodiode is saturated by charging the electric charges to the photodiode using light incident from a light emitting sheet disposed on the backside of the sensor panel. However, in this case, the offset level of the photodiode increases excessively.
In addition, the input terminal of the photodiode is generally connected to a negative bias voltage. In this case, the offset level of the photodiode becomes unstable. For example, electric charges may be unnecessarily charged to the photodiode by leakage current through the switching element for a waiting time.